Brian Behlendorf 86dd0fd922 Pre-allocate vdev I/O buffers ... The vdev queue layer may require a small number of buffers when attempting to create aggregate I/O requests. Rather than attempting to allocate them from the global zio buffers, which is slow under memory pressure, it makes sense to pre-allocate them because... 1) These buffers are short lived. They are only required for the life of a single I/O at which point they can be used by the next I/O. 2) The maximum number of concurrent buffers needed by a vdev is small. It's roughly limited by the zfs_vdev_max_pending tunable which defaults to 10. By keeping a small list of these buffer per-vdev we can ensure one is always available when we need it. This significantly reduces contention on the vq->vq_lock, because we no longer need to perform a slow allocation under this lock. This is particularly important when memory is already low on the system. It would probably be wise to extend the use of these buffers beyond aggregate I/O and in to the raidz implementation. The inability to quickly allocate buffer for the parity stripes could result in similiar problems. Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>		2012-08-27 12:01:37 -07:00
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avl	Add script for builtin module building.	2012-07-26 13:45:09 -07:00
nvpair	Add script for builtin module building.	2012-07-26 13:45:09 -07:00
unicode	Add script for builtin module building.	2012-07-26 13:45:09 -07:00
zcommon	Illumos #1693: persistent 'comment' field for a zpool	2012-08-08 11:49:37 -07:00
zfs	Pre-allocate vdev I/O buffers	2012-08-27 12:01:37 -07:00
zpios	Add script for builtin module building.	2012-07-26 13:45:09 -07:00
.gitignore	Add .gitignore files to exclude build products	2010-01-08 11:35:17 -08:00
Makefile.in	Add script for builtin module building.	2012-07-26 13:45:09 -07:00